Apparatus for packaging in a controlled atmosphere



April 7, 1953 H. A. ROHDIN 2,633,684

APPARATUS FOR PACKAGING IN A CONTROLLED ATMOSPHERE Filed June 5, 1947 5 Sheets-Sheet l awe/M00 Howard A. Rohdin April 7, 1953 I H. A. ROHDIN 2,633,684

APPARATUS FOR PACKAGING IN A CONTROLLED ATMOSPHERE Filed June 5, 194'? 5 Sheets-Sheet 2 Howard A. Rohdin April 7, 1953 H. A. ROHDIN 2,633,684

APPARATUS FOR PACKAGING IN A CONTROLLED ATMOSPHERE Filed June 5, 1947 5 Sheets-Sheet 3 1 F] G gas vacuum Howdrd A. Rohdin Wang H. A. ROH DIN April 7, 1953 APPARATUS FOR PACKAGING IN A CONTROLLED ATMOSPHERE Filed June 5, 1947 5 Sheets-Sheet 4 FIG. I0

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Qvwwrvfom Howard A. Rohdin APPARATUS FOR PACKAGING IN A CONTROLLED ATMOSPHERE FiledJune 5, 1947 H. A. FiOHDlN April 7, 1953 5 Sheets-Sheet 5 FIG. l3

5 2 P Howard A. Rohdin- Patented Apr. 7, 1953 APPARATUS FOR PACKAGING IN A CONTROLLED ATMOSPHERE Howard Rohdin, Glen Ridge, N. J.

Application June 5, 1947, Serial No. 752,773

This invention relates to packaging apparatus.

It is frequently necessary to package materials under controlled atmospheric conditions, that is, the desired condition may range from extremely low'hum'idity to extremel high humidity or it may be desired'to package the material in a particular gas or under vacuum. Where control of humidity conditions is required it is customary at present to air condition the rooms in which the packaging takes place to adjust the humidity to a desired point. When either extreme of humidity is needed the room becomes a most unpleasant place in which to work and in the case of low humidity in particular the effect is quite serious on the physical condition of the workers.

Gas packaging is relatively simple if the gas is carbon dioxide due to its well known tendency to sink through air. When other gases are involved, however, which are either lighter than air or of approximately the same density, difficulties arise and these are particularly hard to overcome when the packaging is done with flexible materials.

Vacuum, of course, is a special case and thus far no one has effectively commercialized a vacuum package with flexible walls.

A principal object of the present invention is the provision of an enclosure immediately adjacent a packaging machine and the control of the atmosphere within the enclosure so as to produce any desired condition. In its further development the invention contemplates providing ingress for the material and egress for the finished packages without disturbance of the controlled conditions within the enclosure.

A further object of the invention is the control of the atmosphere adjacent each machine in a battery of machines with the ability to break the control and enter the enclosure of any one machine without disturbance of conditions in the other machines.

' A still further object of the invention is to provide an apparatus which is largely automatic in operation and which is capable of producing hermetically sealed packages of flexible material having a sealed-in atmosphere of any desired character. An additional object is to provide such a machine which is continuous in operation, and whose speed is such that the cost of operation, per unit package, is relatively small.

The above and other objects and advantages of the invention willbest be understood by referring to the following detailed specification of certain preferred embodiments thereof, taken in connection with the accompanying drawings, in which: I

3 Claims. (Cl. 53-=48) Fig. 1 is a side elevational view of one form of packaging machine in accordance with the invention, parts being broken away;

Fig. 2 is a partial front elevation of the same device, parts being shown in section, the view being taken generally along line 2-2 of Fig. 1;

Fig. 3 is a fragmentary sectional view taken along line 3-3 of Fig. 2;

Fig. 3-A is a view similar to Fig. 3 of a modifled form of sealing element;

Fig. 4 is a fragmentary isometric view illustrating the construction of the sealing unit of Fig. 1 with its lid raised to reveal the interior construction Fig. 5 is a fragmentary sectional view taken along line 55 of Fig. 4, but illustrating the parts as they would appear with the lid closed Fig. 6 is a sectional view taken along line 6--6 of Fig. 4

Fig. 7 is a side elevation of a modified form of sealing and filling unit;

Fig. 8 is a similar View of another modification of a sealing unit, with associated parts;

Fig. 9 is a View similar to Fig. 8 of a further form of sealing unit;

Fig. 10 is a plan view of the unit shown in Fig. 9, a part of the cover of the sealing unit being broken away;

Fig. 11 is a schematic plan view illustrating the stages in the sealing of a package with the unit of Figs. 9 and 10;

Fig. 12 is a side elevation, with parts broken away, of still another arrangement of filling and sealing unit;

Fig. 13 is a schematic plan view of a portion of the mechanism of Fig. 12, to illustrate the manner of travel of the webs therethrough; and.

Fig. 14 is a schematic side elevation of a final form of packaging machine.

Referring now to Fig. l of the drawings, there is illustrated a preferred embodiment of the invention adapted for the production of packages formed of flexible material, such as thin metallic foil, flexible plastic films or the like, and particularly intended to produce such packages in which the volume occupied by the contents is substantially evacuated. As there shown, there is provided a supply roll it] from which is drawn a web i2, as of metallic foil, which passes over a guide roll l4 and thence substantially horizontally beneath a measuring and dispensing unit comprising a hopper It provided with any desired type of measurin and feeding device 58 here shown as driven intermittently, in time relation to the movement of web l2 by a Geneva gear 20, 22 belted or otherwise driven from a motor 24. This unit operates to deposit, in spaced relation upon web I2, a series of piles 26 of the material to be packaged, which may be, as here shown, a pulverulent material, or it may be in tablet or other pro-formed condition.

A second web 28, which may also be of metallic foil or of a suitable plastic film, is supplied from an upper supply roll 3% and thence down over a guide roller 32 which brings web 23 into juxtaposition with web i2, thus forming a kind of sandwich in which the material being packaged is held more or less firmly between the upper and lower webs, in spaced units separated by regions in which the webs are practically or actually in contact. It will be understood that the materialv of which Webs i2 and 28 are formed are either inherently heat scalable, for example, are made of heat-scalable plastic films, or, as in the case of metallic foils, they are provided with heat sealable coatings, as of thermoplastic resinous materials, on those surfaces which will face each other when the webs are juxtaposed.

The heat sealing of the opposed Webs l2 and '28 to one another, here under vacuum conditions, is accomplished within a sealing unit here generally designated by numeral Ed, and comprising a cabinet base portion 36 to which is hingedly connectedawindowed cover portion 33. Opposite ends of this cabinet are provided with hermetic sealing means adapted to pass the webs of material without substantial admission of air to the cabinet, such means being best illustrated in Figs. 2 and 3 as comprising a pair of specially constructed sealing rolls id and 52, mounted respectively on the base portion 35 and cover portion 38 so that their common contacting faces lie substantially in the parting line along which the cabinet 34 may be opened. As shown in Fig. 3, each of these rolls comprises a central shaft M which may be of steel or other metal, surrounded by a. rather thin, solid layer 56 of hard rubber or equivalent material, of high tensile strength, a core portion is formed preferably of a highly resilient material such as sponge or foam rubber, and a thin outer covering 5c of the same material as layer 36, whose outer surface is glazed or slick and highly resilient. These rolls are journalled for free rotation in the respective cover parts, and the shafts of the lower rolls passing through the rear wall of the cabinet base 3t for drive in a manner hereinafter described. The centers of the rolls are so located that the mating faces thereof are compressed together in contact over a lengthwise strip one or one and a half inches wide.

In order to seal the rolls do and 42., at the exit end of the cabinet, and their counterparts M! and 42' at the entrance end, there is provided to bear against each, where it passes through the cabinet wall remote from the parting line, a contact shoe 52, preferably of polished metal or the like, secured in the cabinet wall and arranged to press firmly against the outer surface of each roll. The longitudinal edges of these shoes may be slightly chamfered, as at as, to accommodate bulges in the surface of the rolls caused by pressure between the rolls and the shoes; and the ends of these shoes are hermetically embedded in the front and rear cabinet walls, as at 56 (Fig. 2). In order to seal the side edges of the rolls against the lateral cabinet walls, the end of each roll may have annular recesses adapted to receive annular ridges such as 58 extended outwardly from the cabinet walls. The bearings of shafts is in the walls of the cabinet may be suitably sealed against leakage by packing membersor glands 60 of soft rubber, leather or the like, held in their seats as by cover plates 62. The entrance end of cabinet 34 is provided with a duplicate set of rolls 4!) and i2, and associated duplicate sealing means.

A modified form of sealing means for the webs entering and/or leaving the filling and sealing cabinet is illustrated in Fig. 3-A and is applicable where the tensile strength of the web material is sufiiciently high that it may be subjected to a large pulling force without tearing or stretching. In that figure, the walls 35' and 38' of the cabinet at the points where the seals are located are broadenedout; to form brackets or pockets 54. Within each of these pockets is received a sealing strip formed of a core 23' of soft sponge rubber, similar to the material it of Fig. 3, and having a thin outer coat '55 formed of the same glazed, slick and highly resilient vulcanized rubber as layer 55.1 of Fig. 3. These two opposed sealing members are so arranged as to normally contact one another over a rather wide area, so that they can accommodate the bulges in strips 52 or 28 caused by the material being packaged without permitting any effective leakage of the atmosphere into or out of the cabinet. The actual pressure against the webs resulting from this contact is kept small enough so that the webs can be drawn through without parting, but the area of contact is so large that an effective trap against transfer of the atmosphere is obtained.

Further features of the sealing unit 34 will be best understood by referring to Fig. l, which illustrates the cabinet with its lid or cover 38 in raised position. The hinges for the cover are designated Gt and 6:; respectively, and when the cover is closed, an air tight seal around the parting edges is formed as by a gasket strip (is secured to the top edge of cabinet base 35 and engageable in a mating groove iii in the lower edge of the cover 38. In order to secure the cover 38 firmly in closed position in a hermetic relationship to the base portion, I have provided hasps such as indicated at 72 on the cover, which are engaged by hook-type overcenter clasps i l on the base portion. The construction is best shown in detail in Fig. 5, showing this-latch in cabinet closed position, with the hook portion E5 of clasp It engaged over the top of the hasp l2. Clasp is is pivoted on an operating handle is as at 38, and handle 78 is in turn pivoted as at .82 between the ears of a bracket 84. Thus, when hook ":6 is placed atop hasp l2 and the handle it is turned down to its Fig. 5 position, the cover is locked firmly down upon the base, compressing gasket strip 68 and being held firmly in place since pivot axis so has thereby been moved behind pivot axis 82.

When the space within cabinet 34 is evacuated, a very substantial atmospheric force operates to maintain cover 38 closed, which would, make it extremely dificult to open for any necessary servicing or for other purposes. Also, where, as is contemplated, a plurality of such cabinets may be evacuated from a single air pump system, it would be impractical to shut down the air pump in order to open a single unit. To facilitate opening the cabinet, therefore, I have provided a vacuum release valveshown in Fig. 5 as comprising a valve element normally held closed by the pressure of a spring 88 acting on a washer or shoulder 98 secured to the stem of the valve member 86. This stem projects beyond the-outer face of the front wall of base portion 36, as at '92, in position to be engaged by an extending lug 94 on latch handle l8 whenever the handle is raised to unlatch the cover. Thus, the normal movemeat of 'unlatc'hi'ng the cover: initially serves to break the vacuum in the cabinet. and enables the cover to be raised easily.

Since, where a plurality of units are evacuated by the same pump, the opening of any one cabinet to the atmosphere would seriously overload the pump and hence reduce the vacuum desired in the other units, I provide an automatic valve operable efiectively to shut off the vacuum line of the open unit at least to the extent that the air pump capacity is not overloaded. To this end, the vacuum line 66 from cabinet base 36 is connected to the pump line 98 through an automatic valve unit I00, best shown in Fig. 6. This unit comprises a housing I02 containing a guide member I04 serving to guide the motion of a valve I06 whose lower end is ground to fit a tapered seat element I08 secured to the housing. Aspring I I is seated upon a lower spider element H2 in the housing, and tends normally to urge valve I06 to its upper (unseated) position, as in Fig. 6. Valve I06 has a small central aperture II4; so that, when the pressures in lines 96 and 98 are-about equal, as is the case when a normal vacuum is maintained in the cabinet, air may be freelyexhausted through the valve unit to compensate for unavoidable leakage into the cabinet. If, however, the cabinet is suddenly opened, as above described, a large flow of air throughthe valve unit -commences, forcing the valve 106' onto its seat and throttling this fiow (due to the small size of aperture II4) to such an extent that it is comparable to normal cabinet leakage, which does not overload the air pump or release vacuum in other units connected to the same pump.

When the cabinet 34 is reclosed, this flow of air: through aperture I I4 gradually evacuates the cabinet, reducing the pressure on the upper side of valve I06 ultimately to the point where spring I I0 reopensthe valve, whereupon full pumpand pipe capacity is available to finish the evacuation ata rapid rate.

A small rod-like member II6 is secured to the inner surface of the top of valve unit I00 so as to project loosely through aperture II4 when the valve 106 moves upwardly; this member serves. periodically to clean the aperture and renders the valve unit self-cleaning in this respect. I

Since, as indicated above, it is intended to operate a plurality of vacuum sealing cabinets in each installation, for reasons of economy, the mounting of such cabinets is desirably of a quickreleasable type. I have here shown the use of slot-type foot brackets I18 permitting the cabinet to be slid out of its place merely by loosening four fastening screws at its corners. 7

Within the cabinet, I have provided a pair of heat sealing rollers I20 and I22, journalled in side brackets I24 and I26 secured to the base of the cabinet, Roller I20 maybe a plain metal or (preferably) resilient rubber roller, mounted for vertical adjustment by means ,Ofv crews I20 acting upon journal blocks such as I30. Lower roller I22 is preferably ofmetal, such as steel or brass, andis recessed at, intervals around its periphery as at I32, to accommodate the bulk of the material between the two Webs. This latter roller-may be heated, as by electrical connections I34 via slip rings or other conventional means within a connector box I36 mounted on the front of the cabinet base 36. The other end of the shaft of roller I22 passes through a hermetic seal in the rear wall of base member 36, and extends for connection through bevel gearing I38 with the eri ssha'it 4i! Q iY n I m- EQI IIL. The shaf of rolls 40 and 40 similarly-pass through the rear wall of the base 36 and are geared to the same drive shaft; this arrangement of positive drive means eliminates the necessity of applying any substantial drawing force lengthwise of the webs, which would subject them to excessive strain, as well as possibly deforming the final packages from their normal shape.

Referring now back to Fig. 1, the heat sealed webs pass out of the cabinet 34 between a pair of draw rolls I42 driven by gearing I44 from drive shaft I40, andthence between a pair of cut-off rolls I46 also connected to the drive shaft. The latter rolls are synchronized to sever the composite webs approximately, centrally of each transverse sealing hand between charges of contents, so that the end product is a series ot evacuated packages each' composed of a pair of sheets having .the contents therebetween, and heat sealed together around their entire periphery. v

The principles of the above disclosed method and apparatus may be carried out in numerous modifications, all operating to produce continuous strip-form packages in which the atmosphere packaged along with the product is subject to the same control. In Fig. '7, for example, there is illustrated a machine comprising a sealing cabinet having a top portion I48 and a base portion I50, the former being capable of mechanical latching to the latter by one or more latches I52 similar in all respects to the latches 14 of 1. In this embodiment, the supply rolls I54 and I56 for the webmaterial are located within the cabinet, rather than outside as v in the previous form, and the material supply hopper is mounted within the top portion I48. A lid I60 for this hopper is hermetically sealed thereto, preferably in the plane of the top face of cabinet portion I48, as by screws I62. Measuring and dispensing devices for hopper I58 (not shown) are provided as in the previous form.

The webs from rolls I54 and I56, after the product has been placed therebetween, are sealed together by heat sealing rollers I64 and I66, and the strip of packages'is then drawn'out of the cabinet through sealing rolls I68 and I10 of the form described in connection with Figs. 2 and 3, by apair of draw rolls I12 and I14, and may thereafter be separated into individual packages by cut-off roll I16. A vacuum line .valveI00 and associated apparatus are connected to the sealing cabinet in the manner heretofore described.

The modification just described has the advantage that only one pair of pressure rolls is required, namely those at the exit end of the cabinet. On the other hand, the vacuum atmosphere needs to be broken occasionally to permit the cabinet to be openedfor replacement of the supply rolls I54 and I56, or when lid I60 is removed to replenish the supply of the'prod uct being packaged in hopper I58.

Fig. 8 of the drawings illustrates a form of ma' chine which is adapted to provide continuous filling and sealing of. packages in a controlled atmosphere such that the finished packages contain a quantity of any desired'gas; for example, carbon dioxide or nitrogen. To accomplish this result, the cabinet of the filling and sealing unit is divided into two chambers, in one of which the entrained atmospher between the W-ebs'i removed by evacuation, and in the other of which an atmosphere of the desired gasasurrounds the sealing operation. In this figure, the upper A portion; of the cabinet is designated .by

numeral 'l"18,"andthelowcrby $80., An upper supply roll I82 for'packa'ging web material is mounted outside the cabinet, as is a lower supply roll I84. A filling and dispensing hopper I88, of the general kind illustrated in Fig. 1, perates to dispense measured charges of the p uct onto the lower web, which is then covered by the upper web. The composite strip containing the product then enters the cabinet between sealing rolls I88 and 190. A partition I92, I94 midway of the length of the cabinet contains sealing rollers I96 and I98, which operate to form a gas-tight partition between the right hand chamber 200 of the cabinet, and the lefthand chamber 202. Heat sealing rollers 204 of a kind described above are contained in cham ber portion 202, which portion is provided with a gas supply line 206 for the admission of any desired, preferably low-pressure atmosphere. A pair-of exit sealing rollers 208 and 210 permit the string or strip of packages to pass from the cabinet between a pair or" draw rolls 2I2 and thence optionally between the usual cutter rollers designated at 214. It will be obvious that chamber portion 200 is provided with the same vacuum connection 98 and valve I00 as in the previous embodiments, and that the same provisions for latchin the cabinet closed may be included if desired.

In starting up a machine of the character just described, the cabinet may first be left slightly open while a supply of gas is admitted through pipe 205, suilicient substantially to displace the air therein. Thereafter the cabinet is tightly sealed and space 200 evacuated, Whereupon the drive mechanism may be started to pass the package strip through the device. It should be understood that the pressure of inert gas maintained in portion 202 of the cabinet is merely nominal, that is, sufilcient to ensure that any trivial leakage which may occur is in the direction outward from the cabinet, to prevent dilution of the gas by air entering from outside. The gas may desirably be supplied from a compressed gas supply tank through a usual form of pressure-reducing valve.

Figs. 9, l0 and 11 illustrate a modification of the apparatus in which a principal proportion of the heat sealing around the individual bodies of the packaged product is accomplished before the composite web enters the sealed chamber, which chamber may be of either of the types heretofore described. Referring to Fig. 9 inparticular, the supply rolls 2H? and 2I8 are mounted outside the sealed chamber, and a supply hopper 220 as above described feeds measured charges 222 of the product between these two webs. The area of the opposed webs surrounding three sides of each quantity of the product is heat .sealed together by a sealing roller 224 provided with heating connections 226. in a known way. As best seen in Fig. 10, roller 224 has a plurality of longitudinal ribs 225 so spaced that transverse heat seals 22! (Fig. 11.) are formed between each two charges 222 or the product. The portion of roller 22 i adjacent the lower .edge of the webs (as view-ed in Figs. 10 and 11) is solid, to form a continuous edge seal 229 along this edge. Thus, the charges 222 are sealed around three sides before entry into chamber 228 through sealing rollers 230. Within the cabinet 228 are a pair of heatsealing rolls 232 and 234, of which roll 232 is a relatively narrow or disc-like roll adapted to complete the edge seal 2351, thus forming thafourth sealed side around each charge of material.

Egress of the composite web is sealed by r01 5 236 and 238 as above described in. connection with previous embodiments, and draw rollers :40 and cut-off rollers 242 may be provided for their usual purposes. Obviously chamber 228 may be a vacuum chamber as in Fig. 8. The formation of transverse seals separating the charges from one another prior to passa e of the webs through the pinch of the cabinet entry rolls is particularly advantageous Where the product being packaged is in powder or ranular form, since migration of such material into the space between charges, due to the pressure or wiping action of the entry rolls, is rendered impossible. However, this arrangement is not limited to the packaging of such materials, as it may also be used in packaging tablets or solids of other form.

Figs. 12 and 13 of the drawings illustrate a modification of the invention in which, while the supply rolls for the web material are maintained outside the sealed cabinet, the material hopper and dispensing means may be disposed interiorly thereof. Such an arrangement makes it unnecessary to open the cabinet as frequently as would be the case with the apparatus of Fig. 7, and is particularly advantageous where the material being packaged is adversely affected by atmospheric conditions; for example, where the material is hygroscopic or deliquescent. Scaling the supply hopper within the chamber permits the atmosphere therein to be controlled in the same Way as the general atmosphere in the cabinet.

Referring particularly to Fig. 12, the apparatus there shown comprises a sealed cabinet 2M and supply rolls 246 and 248 outside such cabinet, webs 252 and 254 of packaging material being drawn from these rolls and theme,

in contact, between the entry rolls 250 of cabine t 244. In order to separate the webs from one another to permit the material to be packaged to be deposited therebetween, I provide a pair of vertical guide rollers 256, suitably journalled on fixed supports within'the cabinet, and about which the upper web 25 is passed from its original horizontal plane to a vertical plane. This diversion of the upper web is more clearly shown in schematic form in Fig. 13, where it will be observed that the web is also moved laterally somewhat in order to provide space for the lower portion and exit spout of the hopper 258.

Hopper 258 is provided with the sealed lid 260 as in forms previously described, and the same measuring or dispensing arrangements may be provided to drop measured quantities of material upon the lower web, after which the turned-up web 254 passes under a guide roll 262 which causes it to turn back into a horizontal plane in contact with lower web 252. Heat sealing rollers 264 and 260 then complete the sealing of the individual packages in the strip, after which the strip leaves the cabinet via sealing rolls 268 and passes between draw rolls 210 and/or cutter mechanism 212.

Where it is desired to package materials in strip form in the general way described above, but in an atmosphere of controlled humidity or dryness without the use of a high vacuum technique, a somewhat simplified version of apparatus show-n in Fig. 14 may be utilized. In this figure, a relatively air tight cabinet 2 is illustrated as comprising a space 216 at one end for the storage of a pair of rolls of web material, said space being partitioned off from the remainder of the cabinet by a baffle plate 280 having a narrow slot for the passage of the webs from the supply rolls 282 and 284. The webs entering the central portion of the cabinet pass between guide rolls 285, and thereafter the upper web (designated 288) is turned upwardly and aside by a pair of vertical guide rolls 200 cognate to rolls 256 of Fig. 12. A supply hopper 292 having the usual charge measuring and dispensing means is mounted within the cabinet and operates to deposit charges upon the lower of the two webs, after which web 288 is turned down upon the charges by horizontal guide rolls 294.

' Heat sealing of the charges between the webs is accomplished in a manner known, per se, by rolls 298, after which the webs pass between draw rolls 298 and a cut-01f mechanism 300, the cut off packages falling ihrough an aperture between bafiie plates 302 and 304 into a collection space 306 from which they may periodically be removed through a door 308. An air circulating blower 310 draws air from the interior of the cabinet 2'14, passes it through any conventional form of drying means or desiccator 312, and returns it to the cabinet. Since doors 281 and 308 need be opened only occasionally, and since there is only a small, if any, net pressure differential between the inside and outside of the cabinet, the

entry of moist atmosphere into the cabinet is almost negligible, particularly since the major portion of the cabinet where the filling and closing is being done is bailled off from those portions which are periodically brought into direct com- :3

munication with the outside air. Obviously, the same arrangement is equally well adapted for use where the atmosphere in the package is to be controlled to any desired degree of high or low humidity, and is not necessarily limited to dry packaging.

It will be seen from the above detailed descriptions of particular embodiments of the invention that I have provided apparatus for carrying out all of the objects of my invention in a compact and efficient manner, but I wish it to be understood that many changes and modifications may be made therein without departing from the scope of my invention as defined in the appended claims.

I claim:

1. Apparatus for packaging comprising: mechanism for passing webs of flexible, heat scalable material along predetermined juxtaposed paths; means for depositing between said webs measured charges of a product to be packaged; sealing means operative subsequent to the operation of said product depositing means adapted to seal said Webs hermetically together around said charges; an enclosure for at least said sealing means; substantially hermetic entrance and exit seals for said enclosure, said seals permitting, respectively, ingress and egress for said webs; means for controlling the atmosphere within said enclosure and thereby between said webs and around said charges; the atmosphere within said enclosure being so controlled as to be diilerentiated from the atmosphere of the room in which the apparatus is operated.

2. The invention in accordance with claim 1, in which said atmosphere controlling means opcrates to establish an atmosphere of air at a pressure substantially below the normal atmospheric pressure thereof.

3. The invention in accordance with claim 1, in which said atmosphere establishing means operates to establish an atmosphere of an inert gas at a pressure slightly above the normal atmospheric pressure of air.

HOWARD A. ROHDIN.

REFERENCES CITED The following references are of record in the file of this patent:

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